Railroads are an important part of the national and international infrastructure for travel by people and the transportation of goods. As of 2012 there were approximately 140,000 miles of standard gauge rail in operation in the United States alone, and about 850,000 miles of rail worldwide (https://en.wikipedia.org/wiki/List_of_countries_by_rail_transport_network_size).
As with any infrastructure asset, rails deteriorate over time, and need to be repaired or replaced. This is an expensive and time consuming process. An information disclosure filed with this application reveals the processes and associated apparatuses often used at present or in the past, which in many cases involve the complete replacement of rail sections, and in some cases rail repair/refurbishment. In all cases, the process is costly, time-consuming, and disruptive to commercial rail traffic. Often, sections of rail routes need to be shut down during the repair or replacement and even removed, which slows or disrupts service over those sections and thus is a substantial source of additional economic loss. And, if rails are not removed, the refurbishment needs to be carefully scheduled between the scheduled runs of trains over those rail routes.
U.S. Pat. No. 8,367,960 is one of the few patents in the aforementioned information disclosure which does not require rail removal (although rail removal is presented as an option at element 124), and which fixes more than just the butt welds between rail sections. Rather, U.S. Pat. No. 8,367,960 utilizes a process of cleaning 130, preheating 140, welding 150, post-heating 160, shaping 170 and testing 180, see FIG. 2, and may be applied with the rail left in place.
Although this is preferable to the other prior art approaches, the multiple radial layers of metal illustrated by 20A through 20G in FIG. 4 and also apparent in FIG. 5 are problematic. First, basic mechanical engineering principles rooted in empirical experience teach that having multiple joints between each of the adjacent layers illustrated by 20A through 20G will make these layers more prone to cracking and chipping than if there was simply a single, substantial seamless layer in the radial direction (i.e., the geometric direction of the radial lines 1, 2, 3 in FIG. 5 outward from the center of the railhead). Specifically, each inter-layer joint along the radial direction illustrated in FIG. 4 becomes a fault surface along which chipping and cracking can occur under the weight and vibration of travel by multiple trains in succession.
Second, as evidenced by FIGS. 6A and 6B of U.S. Pat. No. 8,367,960, this radial layering ends up causing substantial hardness variations as a function of depth below the restored rail surface, which variations are “below the AREMA hardness requirement” from about 8 mm to 15 mm in depth, see column 6 lines 45 to 68. To remediate this requires the additional step of post-heating 160 as thereafter described in connection with FIGS. 7 and 8 of U.S. Pat. No. 8,367,960. In effect, the post-heating functions to “temper the existence of martensite” and “to temper the prior weld beads of the multiple welding process. As a result, the surface hardness of the welded metal surface may be about 410 HB to about 450 HB, thereby not only meeting the AREMA hardness requirements but also exceeding the original rail surface hardness by, e.g., approximately 50%. Thus, an anticipated wear life of the restored rail section or a new rail section may be substantially increased,” see column 7 lines 14-26 of U.S. Pat. No. 8,367,960.
Third, the overall refurbishment process is made slower because of the need to apply multiple radial layers, and additionally to post-heat 160 these layers to temper them and overcome the problem of below-standard hardness and susceptibility to cracking and chipping along weld lines, all stemming from the radial layering.
Finally, having the outside rail surface “exceeding the original rail surface hardness by, e.g., approximately 50%” is actually not a desirable outcome. Either the hardness should be substantially-uniform along the radial lines of the rail, or the hardness should decrease as one moves radially-outward toward the railhead surface, which provides some plasticity to the surface contacted by the trail wheels. If the surface harness is substantially greater than the interior hardness as is taught by U.S. Pat. No. 8,367,960, then a sort of “eggshell” configuration is created wherein the outside surface of the rail can “crush” the inside rail under heavy stresses.
It would desirable to be able to only apply a single fill layer in the radial direction, and by doing so, to entirely avoid the above-mentioned radial layering problems. It is also desirable to avoid the need for any form of post-heating, i.e., to entirely omit the need for a post-heating step such as that disclosed by 160 of U.S. Pat. No. 8,367,960.
However, being able to fill the entire cross-sectional area 12B in FIG. 4 of U.S. Pat. No. 8,367,960 with a single layer in the radial direction without having to apply multiple radial layers, and being able to omit any post-heating from the process, presents a nontrivial engineering problem, requiring a non-obvious, inventive solution. This is because consumable fill materials used in welding—when they are hot and still in liquid form just after being applied—will not pool with enough depth to fill a wear pocket along, say, the radius 1 in FIG. 5, which wear pocket (cross section in need of filling) may be a half inch or more above the worn surface of the rail.
Rather, if an attempt is made to fill such a large pocket all in one pass, gravity will spread out and thin the weld pool while drawing the liquefied fill down toward the ground, defeating such an attempt. Thus, fill material applied along the radius 1 in FIG. 5 of U.S. Pat. No. 8,367,960 over the entire region to be filled beyond the worn rail surface would flow down the left side of the illustrated rail and not fill the entire cross-sectional area as desired. This flow problem is why U.S. Pat. No. 8,367,960 notes at column 6 lines 8-10 that the layers are about 0.15 inches apiece: at this reduced depth, the adhesion, surface tension and viscosity of the consumable fill material employed will presumably counteract this flow problem. But this thin layering means multiple radial layers are needed to complete the entire fill. This becomes the source of the radial layering problems discussed above, and is the reason why the post-heating step is needed in U.S. Pat. No. 8,367,960.
It would be desirable in view of the above to have a method and related systems and apparatus components, which enable rail refurbishments to occur in much less time and at substantially lower costs with much less disruption, than do the methods available at present.
And in particular, it would be desirable to make nonobvious improvements to the basic weld process of U.S. Pat. No. 8,367,960, which improvements would enable a single radial layer of fill material to be applied in a single pass to minimize repair time without any post-heating. This would maximize the strength, durability and lifecycle of the railway refurbishment, eliminate susceptibility to cracking and chipping form heavy rail traffic, and allow the refurbishment process to be competed in the shortest time and at the least expense possible.